Electric lampholders

ABSTRACT

A lampholder for a screw-cap electric lamp comprises a socket and supported within the socket a ring of resilient wire which forms the screw thread of the lampholder and which also acts as a first centering means for the lamp. The lampholder is provided with a side contact which includes a number of contact portions spaced circumferentially of the interior of the socket to establish electrical contact with the circumference of the threaded plug of the lamp and also to act as a second centering means for the latter.

Unite States atet Ruston [541 ELECTRIC LAMPHOLDERS Inventor: Reginald Ruston, Birmingham, En-

gland Rowlands Electrical Accessories Limited, Smethwick, Warley, Warwick, England Filed: March 21, 1969 Appl. No.: 809,200

Assignee:

Foreign Application Priority Data March 21, 1968 Great Britain ..13,665/68 US. Cl. ..339/67, 339/93 L, 339/180 Int. Cl. .1101! 7/30 Field of Search ..339/67, 92, 93, 180, 199

Referenca Cited UNITED STATES PATENTS 11/1909 Russel ..339/67 51 Aug. 22, 1972 1,216,884 Thomas ..339/180 1,727,148 9/1929 White ..339/199 3,119,646 l/l964 Adie ..339/67 3,568,133 3/1971 Johnson ..339/64 R Primary Examiner-Joseph l-l. McGlynn Attorney.lohn Harrow Leonard [57] ABSTRACT A lampholder for a screwcap electric lamp comprises a socket and supported within the socket a ring of resilient wire which forms the screw thread of the lampholder and which also acts as a first centering means for the lamp. The lampholder is provided with a side contact which includes a number of contact portions spaced circumferentially of the interior of the socket to establish electrical contact with the circumference of the threaded plug of the lamp and also to act as a second centering means for the latter.

8 Claims, 3 Drawing Figures Patented Aug. 22, 1972 .2 Sheets-Sheet 1 I3 I I Patented Aug. 22, 1972 3,686,621

.2 Sheets-Sheet 2 ELECTRIC LAMPHOLDERS BACKGROUND OF THE INVENTION This invention relates to screw lampholders of the kind comprising a socket provided with a screw thread in the form of one or more rings of resilient wire or rod, with with their sides forming resilient bar-like members, each extending as chords relative to an internal cylindrical surface of a side wall of the socket. Such lampholder also comprises a center electrical contact with a contact portion disposed within the socket adjacent to the center of an end wall of the socket, a side electrical contact and respective terminal means associated with each contact.

An example of such a lampholder is disclosed in our U.S. Pat. No. 3,119,646. The socket of the particular lampholder described and illustrated therein is provided with a screw thread in the form of two rings spaced axially of the socket, both being disposed near a mouth of the socket, and with a side contact comprising a single contact portion disposed adjacent the internal surface of the side wall of the socket and at the end thereof nearest the end wall.

The axially spaced rings collectively forming the screw thread are subjected to axial loading when the lamp is screwed home so that the resilient bar-like members tend to bow towards the mouth of the socket and exert a spring pressure on the screw-threaded plug of the lamp urging a center contact of the lamp into engagement with the center contact of the lampholder. Also the axially spaced rings themselves, by virtue of their axial spacing, provide for centering of the screwthreaded plug of the lamp with respect to the socket and thereby maintain same in co-axial relation with the socket against side thrust exerted on the lamp by the side contact.

Whilst such lampholder is entirely satisfactory and has many advantages over conventional lampholders, certain further problems are encountered as the rated power dissipation of the lamp, for which such holder is intended, increases.

In particular the center contact of the lamp is ordinarily made of a relatively soft metal so that there is no difficulty in maintaining electrical contact over an adequate area between this center contact and the center contact of the lampholder, especially by virtue of the axial spring pressure exerted by the rings, but the screw-threaded surface of the plug of the lamp and which acts as the other lamp contact, is ordinarily made of a harder metal, for example brass, and there is difficulty in maintaining a satisfactory electrically conductive path between the side contact of the holder and the screw-threaded plug of the lamp.

Moreover, the dimensional tolerances of the screwthreaded plug are quite large and, therefore, the side contact of the lampholder has to present sufiicient resilience or spring action to maintain good pressure engagement with the plug of the lamp over a correspondingly large range of lateral displacement. Further, if the contact pressure or stiffness of the side contact is increased to ensure contact over a satisfactorily large area for higher current ratings, there is a tendency for the end of the screw-threaded plug nearest the end wall of the socket to be displaced laterally thereby setting up misalignment between the lamp and the holder and possibly a less satisfactory conductive relation between the center contacts in the lamp and holder respectively.

BRIEF SUMMARY OF THE INVENTION The object of the invention is to provide a new or improved lampholder whereby the above mentioned disadvantages are avoided or reduced.

Accordingly to the present invention we provide a screw lampholder comprising a socket made of electrically insulating, rigid material to receive a screwthreaded plug of a screw-cap electric lamp and having a side wall, an end wall which closes one end of the socket, and within the socket a center electrical contact disposed adjacent the end wall, a side electrical contact and at least one ring of polygonal form to form the sole screw thread in the socket, the ring being made of resilient wire and comprising a plurality of bar-like members extending as chords relative to the internal surface of the side wall of the socket in a common plane which is inclined at an acute angle to a longitudinal axis of the socket, characterized in that the side contact comprises a plurality of contact portions spaced circumferentially around an inner face of the side wall.

The word ring in this specification as applied to triangular or other polygonal forms means such forms in which the sides thereof, which are adjacent each other circumferentially of the socket, may be joined together so as to be continuous or may be separate from each other.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevation and partly in diametrical cross-section on the line 1-1 of FIG. 2 of one form of lampholder in accordance with the invention.

FIG. 2 is a plan view of the lampholder shown in FIG. 1; and

FIG. 3 shows on a reduced scale the stamping which is subsequently bent to form the side contact of the lampholder shown in FIG. 1.

DETAILED DESCRIPTION In this embodiment the lampholder has a body 10 formed of an insulating material such as a ceramic, for example porcelain. The body has a generally cylindrical side wall I I and an end wall 12. Adjacent the mouth of the socket 13 defined by the body the internal diameter is enlarged by forming the internal surface of the side wall 11 with a frusto-conical face portion 14 providing clearance with respect to the glass envelope of a lamp when the screw-threaded plug or cap thereof is screwed home into the lampholder.

The end wall 12 is formed centrally with an integral boss 15 projecting axially from the inner surface of this wall. Such boss serves two purposes, the first of which is to form a backing for a center contact 16 formed from a piece of strip metal and which is provided with a terminal element 17 including a rivet portion 18 by means of which the assembly of terminal element and contact is secured in an opening 19 in the end wall. The terminal element has a passageway 20 to receive a conductor wire and a means for securing the conductor wire such as pinch screw 21 which can be tightened and released through an access hole 22 extending radially through the side wall 11.

The boss also defines, in combination with the end wall 12 and the side wall 1 1, an annular channel 23 in which is disposed a portion of a side contact indicated generally at 24. Such side contact comprises a unitary member formed of strip metal and having a plurality of tongues 25 lying adjacent to, but spaced inwardly from, the inner surface of the side wall 11 at positions spaced apart equally therearound, and situated adjacent to the end wall of the socket.

The tongues 25 are integrally connected with each other by connecting portion 26 which lies against the inner surface of the side wall 11 and is conveniently secured in position partly by rivets 32 and partly by a terminal element 29 (FIG. 2) similar to the terminal element 17 and secured to the bottom wall. Such terminal element is also provided with a pinch screw 30 operable through an access opening 33 in the connecting portion 26. This terminal element would conveniently be positioned adjacent to one of the tongues 25 remote from the terminal element 17.

Although two tongues 25 would provide a degree of self-centering of the screw-threaded plug of the lamp at its inner end, it is preferred that at least three tongues be provided as in the particular example now illustrated wherein as seen in FIG. 2 the tongues 25 are at equally angularly spaced intervals around axis 28.

The connecting portion 26 may be of gapped annular form, the gap providing a space within which the terminal element 17 is positioned.

In the embodiment of the invention now illustrated the end wall 12 is formed with a pair of upstanding ribs 35 each of which is disposed adjacent a respective one of the ends of the connection portion 26 so as to define, in combination with the boss 15, a pocket to receive the terminal element 17.

At least the side contact member, that is to say the tongues 25 and connecting portion 26, is made of a beryllium copper alloy which is resilient and maintains its resilient characteristics for a long service life under high temperature operating conditions. The center contact may also be made of this metal although, for reasons hereinafter explained, a metal having a lesser degree of resilience or negligible resilience could be employed.

At a position spaced axially from the junction of the flaring or frusto-conical portion of the inner surface of the side wall and the cylindrical portion of this surface, there is provided a single ring 27 of resilient metal rod or wire, for example stainless steel wire typically of 1S swg.

This ring is of generally square configuration with somewhat rounded corners, each of the latter being received in a respective one of four grooves formed in the side wall 1 1. The straight limb or wire between corners spans the internal surface of the side wall as a chord and projects radially inwardly of such surface to engage in the grooves of the screw thread of the plug of a screw-cap lamp which is to be screwed into the socket.

The ring 27 has its free ends unconnected with each other and one of these is cranked radially outwardly and engages in a blind hole formed in the internal surface of the side wall, the other free end being received in one of the grooves previously mentioned.

The grooves collectively and the ring 27 lie in a plane oblique to the axis 28 of the holder so as effectively to form one turn of a screw thread.

The positioning of the ring 27 is selected to provide the greatest axial separation between such ring on the one hand and the area of contact of the tongue 25 with the screw-threaded plug on the other hand, so that these two components in combination provide maximum constraint to displacement of the lamp from centered relation with the axis 28, whilst having some degree of axial inset of the ring 27 with respect to the mouth of the holder to guard against inadvertent contact with the hand of a user in screwing a lamp into and out of the holder.

Referring now to FIG. 3, which illustrates the side contact 24, it will be noticed that adjacent tongues 25 are separated by gaps 36 having the same dimensions as the tongues 25. Thus the severing of one side contact 24 from a strip metal stock may simultaneously form the tongues of a second side contact 24, the tongues of the first side contact being interleaved by those of the second side contact and the respective connecting portions 26 being formed from opposite lateral portions of the stock.

Each of the tongues 25 is resiliently retained in its respective position within the socket partly by an adjacent securing tab 37 which projects from the edge of the connecting portion 26 adjacent the end wall 12 of the socket to which it is riveted as hereinbefore described, and partly by the action of the adjacent portion of the connecting portion 26. The latter supports the tongue 25 in a cantilever manner so that resilient movement of that portion of the connection portion 26 which lies adjacent to the tongue 25 contributes to the resilient movement of the tongue itself.

When the screw-threaded plug of a screw-cap electric lamp is screwed into the socket defined by the body 10, the threaded periphery of the plug is engaged at axially spaced positions by the ring 27 of resilient metal rod and the tongues 25 of the side contact respectively. The ring 27 acts as a first centering means and the tongues 25 of the side contact act collectively as a second centering means to center the plug of the lamp accurately with the socket.

When the plug of the lamp is screwed home the respective mid-portions of the limbs of the ring 27 which lie between the corners supported by the side wall 11 of the socket are resiliently displaced axially towards the mouth 13 of the socket. The ring 27 thus exerts an axial force on the plug of the lamp directed towards the end wall 12 of the socket. The center contact 16 is clamped firmly between the boss 15 and the center contact of the plug of the screw-cap electric lamp.

In addition to being displaced axially when the plug of the lamp is screwed home the mid-portions of the limbs of the ring 27 are displaced radially outwardly towards the side wall 1 1 of the socket. The resilience of the wire of which the ring is formed is such as to lock or jam the plug of the lamp against axial withdrawal when the mid-portions of the limbs have been displaced in the manner described.

The side contact 24 may be provided with a connecting portion which overlies the end wall of the socket at a position adjacent to the side wall. In this case the tongues would project from the edge of the connecting portion immediately adjacent the side wall of the socket and the rivets 32 would extend through apertures formed in the connecting portion itself. Altematively the connecting portion may be of annular form, in which case an access opening would be provided adjacent the terminal element 17 and sufiicient clearance would be provided by said opening to establish the necessary electrical insulation between the side contact and the terminal portion of the center contact, the pinch screw associated therewith and any electrical conductor associated with the center contact.

A holder constructed in accordance with the present invention is suitable for use with lamps rated up to 500 volts carrying currents up to 30 amperes.

I claim:

1. A screw lampholder comprising a socket made of electrically insulating, rigid material open at one end to receive an electrically conductive screw-threaded plug forming aside electrical contact of a screw-cap electric lamp provided also with a center contact on the end face of said plug, said socket having a side wall and an end wall to close the other end of the socket, electrical contact means in said socket adjacent said end wall, and screw thread means in said socket, said lampholder including the improvement wherein:

a. said screw thread means comprises at least one ring of polygonal form made of resilient wire and including a plurality of bar-like members extending as chords relative to the internal surface of the socket,

b. said side wall of said socket includes means for supporting the or each bar-like member only at its ends leaving a mid-portion of each of said bar-like members free to undergo displacement radially and axially,

c. said wire having cross-sectional dimensions which are sufficiently large for the wire to lock or jam between said plug and said side wall when said midportions are displaced axially in a direction towards said open end and radially outwardly towards said internal surface thereby to provide positive retention of said plug in said socket against axial withdrawal and to center the engaged portion of the plug in said socket,

d. said electrical contact means includes:

1. a center contact means on said end wall for abutment with the center contact on said plug, a side contact means including contact portions which are distributed around the circumference of the socket in positions radially inwardly of the socket such that, when in engagement with an installed plug, they are in electrical and pressure contact with radially outwardly facing side wall portions of the plug and their pressure forces are directed radially inwardly toward, and substantially normal to, the axis of the socket, and which are positioned axially of the socket in positions such that, when a plug is installed they engage the threaded side wall of the installed plug, and are free from contact with the inner end of the plug, and are in such positions circumferentially of the socket that the combined reactionary radial forces they impose on the plug, when installed, as the result of said pressure contact, center the portion of the plug they engage with respect to the socket, said side contact means being spaced axially from said ring so that, in combination with said ring, they center said plug, when installed, with respect to said socket at positions spaced from each other axially of the socket.

2. The improvement according to claim 1 wherein:

a. a single one of said rings is provided,

b. said single ring is disposed at a position along said interior surface nearer to the open end of the socket than to said end wall.

3. The improvement according to claim 1 wherein the side contact means comprises:

a. a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket,

b. means for connecting said tongues together in the form of a strip of electrically conductive material which overlies the inner surface of the side wall adjacent to the end wall of the socket.

4. The improvement according to claim 1 wherein the side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and formed integrally with a connecting strip disposed adjacent to the end wall of the socket.

5. The improvement according to claim 1 wherein the side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and an integral connecting stn'p disposed adjacent to the end wall of the socket, adjacent tongues being separated by gaps having a width which is at least approximately equal to the width of each tongue.

6. The improvement according to claim 1 wherein said side contact means comprises:

a. a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket,

. means for supporting said tongues resiliently in their respective positions, said means including:

1. a resilient strip formed integrally with said tongues, extending between same, and overlying the inner surface of the side wall adjacent to said end wall of the socket,

2. fastening means for securing a plurality of marginal portions of said strip rigidly to said end wall of the socket, each of said marginal portions being situated on said strip opposite to one of said resilient tongues which extend therefrom.

. The improvement according to claim 1 wherein:

. said side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and means for connecting said tongues together including a connecting strip overlying the inner face of the side wall adjacent to said end wall of the socket,

. said connecting strip is disposed within a channel defined by a central boss which projects axially from the inner surface of said end wall, in combination with the end wall and the side wall of the socket,

plug from the socket, is electrically insulated from the side contact, and (b) the side contact lies wholly within a second zone adjacent to the end wall of the socket and separated from the first zone by an intervening zone.

l I! t l UNHED STATES PA'IENT ()FFECE QETHWCATE OF QUREQTEN Patent No. 3,686,621 Dated August 22, 1972 Inventor(s) Reginald Rus tOll It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 3, line 57, for or" read -of--.

Col. t, after line 1 and before line 15, insert the following paragraph:

-It will be noted that the ring 2? lies wholly within a first zone adjacent to but axially inset from the mouth of the socket. It will also be noted that the side contact member lies wholly within a second zone adjacent to the end wall 12. Between these first and second zones there is an intermediate zone into which neither the side contact member nor the ring 27' eXtends.--

Signed and sealed this 9th day of January 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR.

ROBERT GOTTSCHALK /\ttest1ng Officer Commissioner of Patents )RM PO-IOSO (10-69) USCOMM-DC 60376-P69 Q u 5 GOVERNMENT PRINTING OFFVICEV: 19 69 ssa-s34 

1. A screw lampholder comprising a socket made of electrically insulating, rigid material open at one end to receive an electrically conductive screw-threaded plug forming a side electrical contact of a screw-cap electric lamp provided also with a center contact on the end face of said plug, said socket having a side wall and an end wall to close the other end of the socket, electrical contact means in said socket adjacent said end wall, and screw thread means in said socket, said lampholder including the improvement wherein: a. said screw thread means comprises at least one ring of polygonal form made of resilient wire and including a plurality of bar-like members extending as chords relative to the internal surface of the socket, b. said side wall of said socket includes means for supporting the or each bar-like member only at its ends leaving a midportion of each of said bar-like members free to undergo displacement radially and axially, c. said wire having cross-sectional dimensions which are sufficiently large for the wire to lock or jam between said plug and said side wall when said midportions are displaced axially in a direction towards said open end and radiallY outwardly towards said internal surface thereby to provide positive retention of said plug in said socket against axial withdrawal and to center the engaged portion of the plug in said socket, d. said electrical contact means includes:
 1. a center contact means on said end wall for abutment with the center contact on said plug,
 2. a side contact means including contact portions which are distributed around the circumference of the socket in positions radially inwardly of the socket such that, when in engagement with an installed plug, they are in electrical and pressure contact with radially outwardly facing side wall portions of the plug and their pressure forces are directed radially inwardly toward, and substantially normal to, the axis of the socket, and which are positioned axially of the socket in positions such that, when a plug is installed they engage the threaded side wall of the installed plug, and are free from contact with the inner end of the plug, and are in such positions circumferentially of the socket that the combined reactionary radial forces they impose on the plug, when installed, as the result of said pressure contact, center the portion of the plug they engage with respect to the socket, said side contact means being spaced axially from said ring so that, in combination with said ring, they center said plug, when installed, with respect to said socket at positions spaced from each other axially of the socket.
 2. a side contact means including contact portions which are distributed around the circumference of the socket in positions radially inwardly of the socket such that, when in engagement with an installed plug, they are in electrical and pressure contact with radially outwardly facing side wall portions of the plug and their pressure forces are directed radially inwardly toward, and substantially normal to, the axis of the socket, and which are positioned axially of the socket in positions such that, when a plug is installed they engage the threaded side wall of the installed plug, and are free from contact with the inner end of the plug, and are in such positions circumferentially of the socket that the combined reactionary radial forces they impose on the plug, when installed, as the result of said pressure contact, center the portion of the plug they engage with respect to the socket, said side contact means being spaced axially from said ring so that, in combination with said ring, they center said plug, when installed, with respect to said socket at positions spaced from each other axially of the socket.
 2. The improvement according to claim 1 wherein: a. a single one of said rings is provided, b. said single ring is disposed at a position along said interior surface nearer to the open end of the socket than to said end wall.
 2. fastening means for securing a plurality of marginal portions of said strip rigidly to said end wall of the socket, each of said marginal portions being situated on said strip opposite to one of said resilient tongues which extend therefrom.
 3. The improvement according to claim 1 wherein the side contact means comprises: a. a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket, b. means for connecting said tongues together in the form of a strip of electrically conductive material which overlies the inner surface of the side wall adjacent to the end wall of the socket.
 4. The improvement according to claim 1 wherein the side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and formed integrally with a connecting strip disposed adjacent to the end wall of the socket.
 5. The improvement according to claim 1 wherein the side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and an integral connecting strip disposed adjacent to the end wall of the socket, adjacent tongues being separated by gaps having a width which is at least approximately equal to the width of each tongue.
 6. The improvement according to claim 1 wherein said side contact means comprises: a. a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket, b. means for supporting said tongues resiliently in their respective positions, said means including:
 7. The improvement according to claim 1 wherein: a. said side contact means comprises a plurality of tongues of resilient strip metal spaced apart circumferentially of the internal surface of the socket and means for connecting said tongues together including a connecting strip overlying the inner face of the side wall adjacent to said end wall of the socket, b. said connecting strip is disposed within a channel defined by a central boss which projects axially from tHe inner surface of said end wall, in combination with the end wall and the side wall of the socket, c. Said center contact means includes a portion which overlies the axially presented face of said central boss.
 8. The improvement according to claim 1 wherein (a) said ring lies wholly within a first zone adjacent to the mouth of the socket and, in the absence of a lamp plug from the socket, is electrically insulated from the side contact, and (b) the side contact lies wholly within a second zone adjacent to the end wall of the socket and separated from the first zone by an intervening zone. 